Working with nature: tropicalforest regrowth and its potential for mitigating climate change

The Bonn challenge aims to restore 350 million hectares ofdegraded land by 2030 of which currently almost 100 million hectares has beencommitted through various initiatives. Restoration is a global priority; notonly to restore the productivity of degraded and unproductive land, but alsobecause promoting tree cover will increase carbon uptake from the air intovegetation biomass and soil, contributing to climate change mitigation. Theland area designated for restoration is huge and shows global commitment forthe cause. But how does one go about restoring such vast areas, and, isn’t thatvery expensive?

As part of an international group of researchers, called2ndFOR, we recently stressed the vital role of second-growth forest for landrestoration and climate change mitigation. Second-growth forests are foreststhat regrow after nearly complete removal of forest cover for agricultural use.Second-growth forest has previously been put forward as a potential carbon sinkbut their potential for carbon sequestration has never been quantified at largescale. It turns out that these forests may teach us how to restore the land andtake up vast amounts of carbon while working with nature, instead of against it.Our results were recently published in the prestigious journals Nature and Science Advances.

We reported on the enormous grow-back potential of tropicalforests in Nature.From the analysis on 1500 forest plots from45 sites across Latin America we concluded that carbon uptake is surprisinglyfast in these second-growth forests: After 20 years, these forests had recovered122 tons of aboveground biomass per hectare. This corresponds to an uptake of3.05 tons of carbon per ha per year, which is 11 times the uptake rate of old-growthforests. We also found that the rate of regrowth differed dramaticallyacross the study sites and that this rate is larger in areas with higher rainfall.A map is provided of the grow-back potential of second-growth forests acrossthe Latin American tropics.

In Science Advanceswe reported what this regrowth potential implies for climate changemitigation. The area of second-growth forests in Latin America is substantial: 240million ha, which is 28% of the lowland forest area. Assuming that 100% of thissecond-growth forest is able to persist and grow over the coming 40 years, therewill be an additional 31.1 petagrams of CO2 stored over that timeperiod, which is enough of offset the carbon emissions from fossil fuel use andindustrial processes in these countries in the past 21 years. What isremarkable is that this huge amount of carbon uptake does not require anycostly tree planting or loss of farmlands. This is exclusively based on naturalforest regrowth and only requires protection of the second-growth forestspresent.

So, working with nature provides us with a low-cost andeffective solution for restoring large areas of land and mitigating climatechange. To do so, second-growth forests should be left to regrow, which onlyworks if there is some form of protection (e.g. fencing, fire-breaks). Forestregrowth is not a quick fix, it takes many decades and the carbon benefitsaccumulate over long time scales. At the same time, adequately protecting matureforests is vital for climate change mitigation. Mature forests do not take upcarbon as fast as second-growth forest but they have large amounts of carbonstored in both biomass and soils. If mature forests are not adequately protected,carbon-uptake gains by second-growth forest may be in vain.

As theworld looks for efficient and affordable ways to restore degraded land and combatclimate change these findings tell us that forest regrowth clearly deservesmore attention among (inter)national policy makers than it has received so far.Rather than working against nature we should work with nature; natural regrowthis a cheap and nature-based solution with a tremendous carbon mitigationpotential.